Cylindrically-shaped articles of absorbent material may be adapted to be used as wicks in a wide variety of applications. For example, wicks may be used for liquid transfer and storage applications including ink and lubrication delivery systems, air freshening and perfume delivery, and gas and liquid filtering applications.
A wick conveys a liquid by capillary action, that is, by the force that results from greater adhesion of a liquid to a solid surface than the internal cohesion of the liquid itself. Thus, capillary action can cause a liquid to rise a vertical distance against the pull of gravity. For example, a computer printer may require that lubricating oil be distributed from a reservoir to its moving parts or that ink be distributed from a reservoir to print elements.
For lubrication, an absorbing wick may be placed in a reservoir of the lubricating oil to be transferred. A rotating cam may periodically contact the upper end of the wick to pick up a trace of the oil while the lower end remains in the reservoir. The upper end of the wick is kept saturated with oil by the capillary action of the wick drawing oil from the reservoir. The service life of the moving machinery may be greatly enhanced by this simple yet inexpensive lubrication system.
Prior art wicks designed for lubrication have been made which consist of an absorbent fibrous inner core surrounded by a non-porous plastic outer wrap. Since the core is formed of individual fibers approximately one to two inches in length, the fibers have a tendency to be displaced by the contact with the rotating cam. This initially causes mushrooming of the wick, the result being reduced effectiveness of the liquid transfer process. These fibers may also be picked up by the rotating cam and propagated throughout the machinery, thereby impeding performance or causing internal damage to the machine. Instead of trouble-free equipment operation, frequent service calls to repair and clean the machine are necessary.
A further disadvantage of prior art wicks for lubrication is that the non-porous plastic outer wrap prohibits any absorption of lubricating oil along the submerged length of the wick. For greater liquid volume transfer requirements, the absorption of the prior art wick is limited by the absorption through the surface area exposed only at the end of the wick. Also, if the submerged end of the wick becomes contaminated, the lubricating oil transfer process ceases despite oil remaining in the reservoir.
Porosity of the longitudinal exterior surface of a wick may also be highly desirable in scent dispersing applications, such as for air fresheners. The length of wick exposed to the air may be controlled to regulate the rate of scent release. Porosity of the outer surface may also be critical in the design of filters for gases or liquids.
Candle wicks which operate on the principle of capillary action of melted paraffin are well known in the art. For example, U.S. Pat. No. 2,829,511 to Oesterle et al. discloses a core of extruded cellulose acetate and strands of cotton fibers wound around the core. To help maintain the textile fibers tight around the core, ceresine or other wax-like substance may be applied to the fibers. While a candle wick may be absorbent along its length, it will not be resistant to mushrooming or fraying at an end that is subject to a periodic mechanical contact, such as the contact of a rotating cam in a lubrication application. Therefore, a candle wick is unsuitable for a liquid transfer application where a fray resistant structure is required.
Cylindrically-shaped structures that may be adapted to be used as a wick are known in other fields as well. For example, in the furniture industry, welt cords are often formed by a braided covering surrounding a core material to retain the core material in a consistent cylindrical shape. (A welt cord is a small cord covered with cloth or other textile material, sewed on a seam or border to strengthen it). The welt cord should maintain good flexibility; however, fraying of the cord ends during handling may frequently be controlled to the required degree by the braiding itself or by the addition of a single glue line applied along the length of the cord. When adapted to be used as a wick, the result of the non-unitary structure of the welt cord is fraying and mushrooming of the ends and a reduced liquid transfer efficiency. The single glue line of a braided welt cord may be attacked and dissolved by a variety of oils and solvents. The glue may also contaminate any transported liquid. Accordingly, the structure of the welt cord is unsuitable for use as a liquid transfer wick where fray resistance and chemical inertness are desired.